The object of the invention is to transmit power from a transmitter to a receiver to enable operation of additional circuit elements or components on the receiver even if the receiver does not have any power supply of its own. Such a requirement exists, for instance, in transponders mounted to fast rotating parts, which thus elude a reliable external power supply and in which the use of batteries should be avoided for reasons of minimum maintenance. Such transponders are used, for instance, for electronic control of the tire pressure in motor vehicles as well as to identify moving goods, or as an item protection system to prevent shoplifting.
Prior art systems use inductive methods (near field) or radio waves with a constant carrier for power transmission. Such systems are described in detail, for instance, in the RFID-Handbuch [RFID Manual] by Klaus Finkenzeller, Hanser Verlag. The disadvantage of inductive systems is that the coils for generating and drawing the power require a lot of space and are heavy. In the radio systems, relatively high transmitting power is required to obtain a useable voltage at the detector due to the defined impedance of the electromagnetic field in free space of approx. 377 ohm (which results from the square root of the ratio of the physical constants mu0 to epsilon0) and the drop in the power density squared to the distance. The maximum permissible transmitting power, however, is usually limited due to government restrictions. Impedance conversion after the antenna is furthermore possible only within limits due to the losses that occur-particularly at the higher frequencies. On the other hand, the use of higher frequencies is desirable because of the smaller antenna size, the improved directional effect of the antennae, and the broader available frequency spectrum.
With the method described in Patent DE 19702768 by the same inventor it is already possible to query analog measured values over relatively long distances, a method that is also used for industrial applications. This method, however, is based on a purely analog circuit in the transponder, which requires a substantially lower operating voltage than comparable digital circuits.
It would be desirable, however, to obtain the higher operating voltage required to operate digital circuit elements as well. Since these circuit elements generally require very little current due to the use of CMOS technology, the object of the invention is to increase the provided voltage at the cost of the maximum available current while keeping the available output constant.
Such components are sufficiently known as voltage transformers, although the employed circuits again function only starting from a certain minimum voltage because the clock generators are otherwise not stimulated to oscillate. On the other hand, the radio frequency is typically not suitable as the clock frequency because it is much too high for this purpose.
The present invention relates to a device or system for wireless power transmission, particularly a system for supplying transponders, including at least one high-frequency transmitter and at least one high-frequency receiver, each of which is connected to at least one antenna, wherein the receiver obtains its operating power from the transmitted high-frequency output, wherein the high-frequency transmitter is modulated with at least one converter clock suitable for a DC-DC converter, the receiver has at least one detector for demodulating the converter clock, the receiver generates a DC operating voltage for at least one DC-DC converter from the high frequency using at least one rectifier or detector-which may also be identical with a detector for demodulating the converter clock, the DC-DC converter using the transmitted converter clock, and generating another DC voltage to operate further circuit elements.